FIGS. 11 and 12 show a conventional elevator apparatus disclosed in, for example, Japanese Unexamined Patent Publication No. 7-117957. The disclosed elevator apparatus is of the traction sheave type wherein a main cable is wound over a drive sheave, and a cage and a counterweight are moved up and down in opposite directions. The elevator apparatus employs, as a winder, an outer rotor motor. FIG. 11 is a perspective view of the elevator apparatus, and FIG. 12 is an enlarged sectional view of a drive machine shown in FIG. 11.
Referring to FIGS. 11 and 12, denoted by numeral 1 is an elevator pit, 2 is a cage, 3 is a cage guide rail vertically provided as a pair within the elevator pit 1 for guiding both sides of the cage 2 so that the cage moves up and down along a predetermined path, 4 is a counterweight, 5 is a counterweight guide rail vertically provided as a pair within the elevator pit 1 for guiding both sides of the counterweight 4 so that the counterweight moves up and down along a predetermined path, and 6 is a braking device associated with the counterweight 4 and tightly pressed against the counterweight guide rails 5 for applying a brake as the occasion requires. Numeral 7 denotes a support beam provided at the top of the elevator pit 1, and 8 denotes a winder comprising an outer rotor motor provided at the top of the elevator pit 1.
As shown in FIG. 12, the winder 8 mainly comprises a stationary shaft 9 having opposite ends supported by and fixed to the support beams 7, an armature iron-core 11 fixed to the shaft 9 and having armature coils 10 wound over the same, and a rotor 12 rotatably supported by the shaft 9 and constituting a drive sheave.
The rotor 12 includes a field iron-core 13, a field permanent magnet 14, a drive sheave 16 having cable grooves formed in its outer periphery, and bearings 17 disposed between the rotor and the shaft 9 for rotatably supporting the former relative to the latter. Numeral 18 denotes an elevator main cable wound along the sheave groove 15, the main cable having one end coupled to the cage 2 and the other end coupled to the counterweight 4. Numeral 19 denotes a braking device associated with the rotor 12 for stopping the rotor 12.
Numeral 20 denotes an absolute value encoder in the form of a ring. The absolute value encoder 20 is arranged such that it surrounds a projected flange of the rotor 12, is joined to the projected flange of the rotor 12 through a bearing 21 for free rotation of the rotor 12, and is fixed through a mounting fixture 23 to an encoder holder 22 which is secured to the shaft 9. Numeral 24 denotes a supporting fixture provided on each of the support beams 7 on both sides for supporting the shaft 9.
In the drive machine thus constructed, the magnetic pole position of the field permanent magnet 14 is detected by the absolute value encoder 20, and the phases of currents supplied to the armature coils 10 are controlled in accordance with the detected result. Also, the rotating speed and the rotating direction of the rotor 12 and hence the drive sheave 16 are detected by the absolute value encoder 20 in order to control the rising/lowering speed and the moving direction of the cage 2.
In not only such a synchronous motor using a field permanent magnet, but also other electric motors such as the so-called three-phase induction motor, it is important to detect the rotational angle of a rotor with respect to a field magnet in a circuit driving control for any of those motors.
The above-described conventional drive machine for elevators has problems below. Supposing, for example, that the absolute value encoder 20 directly attached to the shaft of the winder malfunctions and has to be replaced, because the absolute value encoder 20 is in the ring form, it is required to dismount the entirety of the winder 8 by moving the shaft 9 upward so as to be withdrawn from the supporting fixtures 24 fixed to the support beams 7, thus resulting in troublesome work. In addition, when the winder 8 is mounted at the top of the elevator pit 1, scaffolding must be temporarily built up, which renders the replacement work more troublesome.
Further, because the absolute value encoder 20 is in the ring form and arranged in a surrounding relation to the projected flange of the rotor 12, its inner diameter is so large that an inexpensive absolute value encoder, which is usually employed in general motors having rotary shafts, is not usable. This raises another problem that the absolute value encoder 20 must be a custom and expensive product.
Still another problem is that because the magnetic pole position of the field magnet is indirectly determined by the absolute value encoder 20 surrounding the projected flange of the rotor 12, the accurate magnetic pole position of the field magnet cannot be obtained.
The present invention has been accomplished with the view of solving the-problems set forth above, and its object is to provide a drive machine for elevators which can determine the accurate magnetic pole position of a field magnet, and can facilitate maintenance work for a detecting unit to detect the magnetic pole position, the rotating speed and the rotating direction of the field magnet.